1. Field of the Invention
The present invention relates to a driving device and a method of driving a washing machine. More particularly, the present invention relates to a driving device and a method of driving a washing machine which enhances the efficiency of an inverter and increases the capacity of the inverter by providing a steady flow of current to the motor to improve the energy loss of the motor and reduce manufacturing costs.
2. Discussion of the Related Art
In general, a pulsator type washing machine is an apparatus which removes various contaminants attached to laundry using an emulsification of detergent, frictional force of water flow due to the rotation of pulsator blades, and agitation applied to laundry by the pulsator. In the pulsator type washing machine, a quantity and type of laundry are detected by a sensor. A washing cycle is automatically determined by a microcomputer in the washing machine based on the quantity and type of laundry. Washing water is supplied to a proper level based on the quantity and the type of laundry, and the washing cycle is performed under the control of the microcomputer.
A drum type washing machine is an apparatus for washing laundry using frictional force between the laundry and a drum rotated by the driving force of a motor where the laundry, water, and detergent are present within the drum. In the drum type washing machine, the drum is rotated and the contaminants are removed due to the beating and rubbing of the laundry inside the drum. Damage and entanglement of the laundry is minimized in a drum type washing machine.
Related Art drum type washing machines utilize one of two different driving methods: an indirect drive method and a direct drive method. In an indirect drive method, the driving force of the motor is indirectly transmitted to the drum via a motor pulley and a belt wound around the drum pulley. There is significant energy loss and noise produced during the transmission of the driving force in an indirect drive method.
In order to solve the problems of the indirect drive method, it has been a growing trend for the related art drum type washing machines to employ a direct drive method for driving the drum. The rotor of the motor is directly connected to the rear wall of the tub in a direct drive method, such that the driving force of the motor is directly transmitted to the drum.
The structure of the related art direct drive drum type clothes washing machine will be briefly described with reference to FIG. 1.
FIG. 1 is a vertical sectional view illustrating the structure of a related art direct drive drum type washing machine. The related art direct drive drum type washing machine includes a tub 2 installed in a cabinet 1, a drum 3 installed in the tub 2, a shaft 4 coupled with the drum 3 to transmit the driving force of a motor 5 to the drum 3, and bearings—(not shown) installed around the ends of the shaft 4.
A door 21 is installed to a front side of the cabinet 1 and a gasket 22 is installed between the door 21 and the tub 2.
A hanging spring 23 is installed between the upper side of the cabinet 1 and the upper outer circumference of the tub 2 to support the tub 2, and a friction damper 24 is installed between the lower side of the cabinet 1 and the lower outer circumference of the tub 2 to dampen vibration of the tub 2 generated during the spin mode.
The motor 5 includes a stator 7 coupled with a rear wall 200 of the tub 2 and a rotor 6 to surround the stator 7. The driving force of the motor is directly transmitted to the drum 3 via the shaft 4. In other words, an additional pulley and belt are not needed to transmit the driving force, because the drum 3 is directly driven.
The motor 5 employed in a washing machine is typically a variable speed motor in which the rotation speed and/or the rotation direction can be controlled. Recently, a permanent magnet type motor, particularly a brushless DC (BLDC) motor has been widely used.
The BLDC motor includes a rotor which forms a field and transmits a torque to the stator of the motor. A stator coil is wound around the stator such that a rotational magnetic field is generated due to interaction with the field from the rotor to generate a torque, whereby a magnetic circuit is formed. A position detector to detect a rotation position of the rotor may also be included in the BLDC motor.
The motor of the washing machine is driven by the microcomputer which controls the motor according to predetermined washing cycles, such as a washing mode, a spin mode, and a rinsing mode. The control of the motor includes control of the rotation speed, torque, and rotational direction of the motor.
Hereinafter, a driving device and a driving method of the related art drum type washing machine will be described with reference to FIG. 2. FIG. 2 is a circuit block diagram illustrating a driving device of a conventional drum type washing machine that includes a conventional BLDC motor.
As illustrated in FIG. 2, the driving device of the related art drum type clothes washing machine includes a rectifier 11, a capacitor 12, an inverter 13, a rotor position detecting circuit 15, a microcomputer 16, and an inverter driving unit 17.
The rectifier 11 receives and rectifies a single phase alternating current voltage into a direct current voltage. The capacitor 12 functions as a smoothing capacitor thereby smoothing the rectified direct current voltage.
The inverter 13 converts the direct current voltage smoothed by the capacitor 12 into a predetermined alternating current voltage according to respective phases, and the motor 5 is driven by the voltage supplied by the inverter 13.
In order to drive the BLDC motor, the position of the rotor must be matched to a phase of the supplied voltage. Thus, in general, a rotor position detecting circuit 15 to detect the position of the rotor is needed. The rotor position detecting circuit 15 includes a sensor to detect a position of the rotor, and recently in the art, the position sensor has included a Hall sensor (not shown).
A Hall sensor detects the position of the rotor by monitoring the rotation of the position detecting permanent magnet installed in an extended line of a rotation shaft of the motor.
Alternatively, without the position detecting permanent magnet, the rotor position detecting unit may be configured to detect the position of the rotor during the rotation of the permanent magnet of the rotor.
The microcomputer 16 compares the position of the rotor detected by the rotor position detecting circuit 15 with a predetermined rotation speed and outputs a signal to control the rotation speed of the motor according to a result of the comparison.
According to the control signal output from the microcomputer 16, the inverter driving unit 17 generates an inverted driving signal such that voltages of respective phases are supplied by the inverter 13 to the motor by the pulse width modulation (PWM) to control the rotation speed, torque, and the rotation direction of the motor.
The method of operating of the related art driving device of a drum type washing machine having the structure as described above will be described as follows.
First, when a single phase alternating current voltage (generally, 220 V, 60 Hz) 18 is input to drive the motor, the rectifier rectifies the input alternating current voltage and outputs the rectified alternating current voltage.
The capacitor 12 smoothes the voltage rectified by the rectifier 11 and converts the rectified voltage into a predetermined direct current voltage (generally 310 V). The inverter 13 converts the rectified direct current voltage into predetermined alternating current voltages and outputs the converted voltages to respective phases of the motor according to a signal of the inverter driver 17.
Due to the alternating voltages converted by the inverter 13, electric currents flow through stator coils wound around the respective phases of the stator u, v, and w, and a rotating magnetic field is formed due to the interaction between a magnetic field formed by the currents and the permanent magnet so that the rotor rotates and is synchronized with the rotating magnetic field.
The rotor position detecting circuit 15 detects the position of the rotor according to the predetermined alternating current voltages from the respective phases and outputs the detected result.
The microcomputer 16 compares the position of the rotor detected by the rotor position detecting circuit with a predetermined rotation speed of the rotor. A control signal is then output by the microcomputer to control the motor according to the result of the comparison.
The control signal output from the microcomputer 16 drives the switching components Q1 to Q6 of the inverter through the inverter driving unit 17. In other words, the switching components are turned on/off to control the magnitudes of the alternating current voltages applied to the motor by Pulse Width Modulation (PWM). By doing so, the magnitude of current applied to the motor is controlled, thus controlling the motor.
Hereinafter, the PWM for driving the motor will be described with reference to FIG. 3. FIG. 3 is a graph illustrating a principle of a sine pulse width modulation (sine PWM).
For the sine PWM, an oscillator is needed to oscillate a carrier wave such that the carrier wave serves as a reference to which the sine wave is compared. In general, a triangular wave is used as the carrier.
The sine PWM compares the triangular wave with the sine wave to a pulse wave corresponding to the comparison, wherein a frequency of the pulse wave is identical to a frequency of the triangular wave.
The sine wave is a predetermined output voltage of the inverter, namely, a reference voltage to be applied to the motor through the inverter for the control of the motor, in a current state. The carrier wave is a voltage to be compared with the reference voltage for the PWM, and generally has a frequency of a few kHz to several tens kHz and usually has a frequency of about 16 kHz for the driving of the drum type washing machine.
As illustrated in FIG. 3, when a PWM wave is generated by comparing the carrier with the reference voltage, the pulse widths of the respective phases vary according to the magnitude of the sine wave.
In other words, for example, when the reference voltage is higher than the carrier wave at phase u of the motor, a high switch component Q1 is switched on so that a high voltage is applied thereto, and conversely a low switch component Q2 is switched on so that a low voltage is applied thereto. As a result, the width of the pulse train is varied according to time when being compared with the reference voltage to be controlled. However, at that time, when an average value of the pulse width modulated waves is estimated, the average value becomes identical to the reference voltage.
The reference voltage does not always take a sine waveform. The magnitude and frequency of the reference voltage are varied such that a necessary electric power can be obtained according to a circumstance during the driving of the motor.
The PWM is a method of converting the reference voltage of an analog waveform into a pulse train with a predetermined frequency such that an average voltage applied to the motor is controlled and as a result, a current flow to the motor is controlled, for example, the direction and a magnitude of the current are controlled. Additionally, a torque is controlled by controlling the current.
The PWM for driving the motor is derived from a driving method of a power module, and according to the PWM, when the power module is controlled by a reference value (the reference voltage) of an analog waveform, the power module is operated within an active area so that a great deal of loss and heat occurs.
Thus, the PWM is used to control voltage and current in a saturation region and a cut-off area of the power module to minimize the power loss and consequently, heat produced by the motor.
However, even when the motor is driven by the PWM, the loss of power occurs due to the inverter, and a majority of the loss is caused by periodically switching the switches of the inverter.
The switching loss will be described in detail with reference to FIG. 4.
First, when the power module is switched on and the current flows therethrough, the current I is restricted by an internal resistance of the power module and an overall resistance of the motor. The voltage applied to the switch is only a voltage loss due to the internal resistance of the power module and an applied voltage is applied to an entire load.
When the power module is switched off, the entire applied voltage is applied to the switch and current does not flow. In other words, as the power module is toggled between on and off, any one of the voltage and current becomes almost 0 (zero). Thus, it has been assumed that there is no power loss.
However, as illustrated in FIG. 4, a significant power loss occurs during a transient period when the voltage and current applied to the power module is toggled between on and off. As a result, a power loss occurs and the power loss is mostly converted into heat inside the motor.
Although the power loss illustrated in FIG. 4, is shown to occur between when the power module is turn off and turned on, a power loss also occurs during the toggle period when the power module is switched from on to off.
The efficiency of the inverter is deteriorated due to the loss of power during the toggle periods and increased temperature of the inverter due to the power loss that is converted into heat. Thus, the operating range of driving the motor is restricted.
Moreover, since an inverter having a large capacity must be used and/or a heat radiator must be used in order to solve the above-mentioned problems, the size of the driving device of the drum type washing machine must be increased. Thus, the manufacturing costs of the washing machine are increased.
Therefore, there is a need for a driving device of a drum type washing machine that reduces the power loss during the toggle period of the inverter and reduces the cost of manufacturing the washing machine.